The prior art has seen a wide variety of different approaches to consolidating proppants injected into fractures.
Hydraulic fracturing of a formation adjacent a borehole increases productivity of desirable hydrocarbonaceous fluids from the subterranean formation by creating channels of high fluid conductivity. In fracturing of formations, two major difficulties have been encountered. The first of these is proppant flowback. This decreases the amount of proppant holding the fractures open, allowing closing of the fractures and causing reduced permeability. The second problem is sand production from the subterranean formation. The produced sand tends to lower productivity, also.
Resin-coated proppants which have the ability to consolidate downhole have the potential to minimize both problems. Most of the commercial resin-coated proppants systems in use today are heat cured and are therefore consolidateable at higher temperatures and pressures found in deep wells.
This leaves a crying need for consolidation of proppants about low temperature wells such as those found in Alaska.
It is desirable to have a relatively high strength so as to resist crushing of the proppant when consolidated. In this way, the proppant is retained in the formation, is not produced back into the borehole or the like. Resin-coated proppants consolidated downhole have been used to offset this problem.
Any resin-coated proppant should be compatible with the fracturing fluids used to carry it downhole and be as economical as possible. Moreover, extra steps should be curtailed when feasible and eliminated where possible, as will be discussed in more detail hereinafter.
The prior art has ranged from U.S. Pat. No. 3,851,479 showing sealed porous earth formations where the void spaces are reduced with the treatment with aqueous solutions containing hydroxyl ions, polyisocyanurates, and polyvinyl alcohol, through U.S. Pat. No. 4,114,382 concerned with consolidating geological formations with a polyol and a special 1,2 alkylene oxide, to recent patents; such as U.S. Pat. No. 4,719,002 describing a method for preparing a molded reaction injection rigid non-cellular polyisocyanurate and U.S. Pat. No. 4,731,427 describing a method of preparing a molded reaction injection rigid polyurethane modified isocyanurate polymer composition. While these patents are pertinent chemically in that the reactants initially are quite similar, the result is vastly different from the invention herein.
It is desirable that any method of coating a proppant to provide downhole consolidation have the following features not heretofore provided:
1. A problem encountered during experimentation to try to solve the problem of consolidating a resin-coated proppant has been that the shearing of the resin-coated proppant causes the resin to come off the proppant and results in little or no consolidation;
2. Another problem has been that, when simulating shearing action that the coated proppant will undergo before or during pumping downhole, the turbulent motion should not cause premature polymerization of the resin. Expressed otherwise, polymerization should not be occurring at this time. It is desirable that a reduced degree of reactivity of any coating be achieved so it does not come off the proppant when admixed with the carrier;
3. It is desirable that the system for consolidating proppant be applicable to either a one step method in which a catalyst is admixed with the admixture of diluent, prepolymer, and proppant or a two step method in which the sand that is coated with the prepolymer and diluent, can be injected and then a catalyst overflushed, or flushed as a minor proportion of a carrier liquid. It is also desirable that the coated proppant have properties set forth in a co-pending application Ser. No. 304,325, now U.S. Pat. No. 4,920,192, filed the same date by Robin Wiser-Halladay as inventor and entitled "A POLYURETHANE QUASI PREPOLYMER FOR PROPPANT CONSOLIDATION". The descriptive matter of that application is incorporated herein in abbreviated form so that the reader will not have to advert to that application; but, in any event, is incorporated herein by reference for any details that may have inadvertently been omitted herefrom.
It is apparent that the prior art has failed to provide the above delineated features, as well as provide a proppant that has been resin-coated and that will cure by what has been abbreviated as a one pass procedure or two pass procedure, and that can be cured in low temperature wells.